In order to regulate the speed of an electric locomotive, thyristors included in AC to DC converters are controlled by firing signals. Since the AC to DC converters generate high harmonic frequency currents which form a psophometric disturbing current, it is necessary to provide a power factor controller to reduce the psophometric disturbing current as well as to improve the power factor of the electric locomotive. Many examples of earlier efforts to provide a power factor controller are described in references such as Japanese Pat. Laid-open Nos. Sho 55-100037, Sho 56-19305 and 56-42819, etc. Although some of these references disclose concepts of merit, currently available power factor controllers require more improvement.
It is desirable for a power factor controller to have three characteristics as follows:
(1) small size because the locomotive has very limited space;
(2) ability to reduce the psophometric disturbing current to under a predetermined value; and
(3) ability to prevent over-compensation which might change a lagging power factor into a leading power factor.